Wellbore logging tool assembly

ABSTRACT

A logging tool assembly comprises an elongate sensor assembly, a plurality of sensor transportation apparatuses for transporting the elongate sensor assembly through a wellbore, and an orientation structure. The sensor transportation apparatuses are spaced apart along the elongate sensor assembly. Each sensor transportation apparatus comprises an engagement structure to connect the sensor transportation apparatus to the elongate sensor assembly and prevent relative rotation between the sensor transportation apparatus and the elongate sensor assembly, and one or more pairs of wheels arranged to rotate on an axis of rotation substantially perpendicular to a longitudinal axis of the elongate sensor assembly. The axes of rotation of the pairs of wheels of said transportation apparatuses are parallel. The orientation structure is connected to the elongate sensor assembly to prevent relative rotation between the orientation structure and the elongate sensor assembly. The orientation structure comprises at least one radially extending orientation projection. In a transverse outline of the logging tool assembly a said orientation projection extends between the pair of wheels so that the shortest distance between a centre of gravity of the elongate sensor assembly and the wellbore wall is when the pair of wheels of the transportation apparatus is in contact with the wellbore wall.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-part application of Ser. No.15/825,074 filed Nov. 28, 2017, which is a Continuation of Ser. No.14/441,833 filed May 8, 2015, which is a National Stage of InternationalApplication No. PCT/NZ2013/000210, filed Nov. 15, 2013, the contents ofall of which are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to apparatus and methods for use in transportingsensor equipment, and in particular to apparatus and methods for use inwireline logging applications.

BACKGROUND ART

Hydrocarbon exploration and development activities rely on informationderived from sensors which capture data relating to the geologicalproperties of an area under exploration. One approach used to acquirethis data is through wireline logging. Wireline logging is typicallyperformed in a wellbore immediately after a new section of hole has beendrilled. These wellbores are drilled to a target depth covering a zoneof interest, typically between 1000-5000 meters deep. A sensor package,also known as a “logging tool” or “tool-string” is then lowered into thewellbore and descends under gravity to the target depth of the wellborewell. The logging tool is lowered on a wireline—being a collection ofelectrical communication wires which are sheathed in a steel cableconnected to the logging tool. Once the logging tool reaches the targetdepth it is then drawn back up through the wellbore at a controlled rateof ascent, with the sensors in the logging tool operating to generateand capture geological data.

There is a wide range of logging tools which are designed to measurevarious physical properties of the rocks and fluids contained within therocks. The logging tools include transducers and sensors to measureproperties such as electrical resistance, gamma-ray density, speed ofsound and so forth. The individual logging tools are often combinableand are typically connected together to form a logging tool-string.These instruments are relatively specialised sensors, which in somecases need to be electrically isolated or located remote from metallicobjects which are a source of noise in the data generated. Some sensorsare designed to make close contact with the borehole wall during dataacquisition whilst others are ideally centred in the wellbore foroptimal results. These requirements need to be accommodated with anydevice that is attached to the tool-string.

The drilling of wells and the wireline logging operation is an expensiveundertaking. This is primarily due to the capital costs of the drillingequipment and the specialised nature of the wireline logging systems. Itis important for these activities to be undertaken and completed aspromptly as possible to minimise these costs. Delays in deploying awireline logging tool are to be avoided wherever possible.

One cause of such delays is the difficulties in lowering wirelinelogging tools down to the target depth of the wellbore. As the loggingtool is lowered by cable down the wellbore by gravity alone, an operatorat the top of the well has very little control of the descent of thelogging tool. Logging tools can become held up on ledges of rock formedinside a well—usually found at the boundaries of hard rock layers wherethe adjacent rock layer crumbles. An operator may not immediatelyidentify that a logging tool has become stuck on a ledge, and may alsospend a significant amount of time reeling the cable and tool-stringback in and attempting to move it past the obstruction formed by aledge.

The chances of a wireline logging tools getting stuck or being impededis also significantly increased with deviated wells. Deviated wells donot run straight vertically downwards and instead extend downward at anangle. Multiple deviated wells are usually drilled from a single surfacelocation to allow a large area of interest to be explored. As wirelinelogging tools are run down a wellbore with a cable under the action ofgravity, the tool-string will traverse the low side or bottom of thewellbore wall and immediately encounter any obstructions on the wellborewall as it travels downwards to the target depth.

Furthermore, in deviated wells there is the potential for drillingcuttings to collect on the low side of the wellbore. Rock cuttings aremore difficult to remove when the wellbore is deviated. The logging toolhas to travel over or through these drilling cuttings, which can impedeits progress and also collect in front of the logging tool. In somecases the logging tool may not be able to plough through the cuttings toreach the bottom of the wellbore.

Furthermore, as hole deviation increases, the sliding friction canprevent the logging tool descending. The practical limit is around50-60° from the vertical, and in these high angle wells any device thatcan reduce friction is very valuable. The running of the tool-stringover the low side surface of the borehole also needs to be taken intoaccount in the design of the tool-string, and in particular the housingand the containment of its sensitive sensors and transducers.

Attempts have been made to address these issues in the deployment ofwireline logging tools, as disclosed in U.S. Pat. Nos. 7,866,384,7,395,881 and US patent application 20120061098. These patentspecifications describe a number of different forms of an in-line rollerdevices integrated into the logging tool-string. These devices aim toreduce the friction experienced by a tool-string as it is run along thelow side slope of a deviated wellbore.

This in-line positioning of roller devices increases the potential tocause damage to the logging tools as there are additional O-ringsconnections required that could potentially leak.

Furthermore, there are multiple additional electrical connections thatneed to be made between the individual logging tools making up thelogging tool-string. The additional components and tool-string lengthmeans it takes longer to connect and disconnect the tool-string, whichslows down the wireline logging operation and therefore increases wellcosts. Further, there is a lack of flexibility inherent in this approachas in-line roller devices can only be placed between logging tools, andas some of these tools are quite long, in-line rollers may not keep theentire tool body off the borehole wall.

The rollers employed in these forms of prior art devices also haverelatively small wheels with a minimal clearances. In deviated wellboreswell drilling cuttings will collect on the low side of the well, andthese small sets of rollers can struggle to make headway through pilesof cuttings. In situations where large amounts of cuttings areencountered these small rollers can be of no assistance at all andsimply add to the length and weight of an already unwieldy tool.

McNay U.S. Pat. No. 8,011,429 and Schlumberger patent applicationUS2013248208 describe roller assemblies which slip over the loggingtool, and are mounted such that they are free to rotate about thelongitudinal axis of the tool. These devices have relatively smallwheels which do not rotate easily over rough surfaces. In addition, itis often the central or side part of the wheel which is in contact withthe wellbore wall, rather than the circumferential or radially extremeedge. This means that the wheels are often skidding rather thanrotating. Neither of these devices has an active lubrication systemwhich can prevent contaminants from entering and jamming the bearings.

All of these existing prior art devices attempt to assist a tool-stringin travelling down a deviated wellbore. However, the devices do notassist in maintaining a known orientation of the tool-string, or aspecific clearance or “standoff” between the active part of thetool-string and the wellbore wall.

U.S. Pat. No. 684,732 describes a sectional threading rod which isprovided with wheels to reduce friction as the rod is pushed down aconduit. The wheels have an axle which is above the centre of the rod.However, the rod is not intended for use with a logging tool.

Other attempts to address the issues associated with deviated wellboresinclude a number of prior art “hole finding” devices. For example USpatent U.S. Pat. No. 4,474,235, US patent application US 20120061098,PCT publication WO 2010/106312 and US patent application US20120222857all describe systems for wireline hole finding devices which rely on oneor more rollers located at the nose at the bottom of a tool-string. Thenose is the leading end at the bottom of the tool-string during descentof the wellbore. These rollers are arranged to allow the nose of thetool-string to roll into, and then up and over, irregularities andobstructions in a wellbore.

However due to the use of a number of metallic components these types ofhole finding devices are not necessarily compatible with induction typeresistivity tools which are generally the most commonly used sensor insuch applications. Also, some logging tools are “bottom only”, and havesensors which must be located at the lower extremity of the tool-string.The prior art hole finders are heavy and metallic and hence notcompatible with such tools.

Furthermore, these systems are relatively complicated and must beappropriately designed and maintained to withstand the hostileenvironment experienced at depth in exploration wells. If the movingparts used in these systems cease to function the hole finder isineffective. These designs are also relatively heavy and inflexible. Anyimpact forces or torque acting on the hole finder are transmitted intothe tool-string, potentially causing damage to the sensors.

Another approach used in the design of hole finding devices is disclosedin US patent application US 20090145596. This patent specificationdescribes an alternative hole finding system employed outside ofwireline applications where a conduit, tubing or pipe is attached to thesensor tool in order to push it down the wellbore. This specificationdiscloses a relatively complicated system which requires a surfaceoperator to actively adjust the orientation of a nose assembly mountedat the bottom of the tool. The specification also discloses that thisdevice requires a range of sensors that are used to detect sensor toolmovement, and specifically if the sensor tool is held up. This form ofhole finding system is again relatively heavy and complex. Furthermore,a dedicated operator is also required to monitor the progress of thesensor tool to actively adjust the orientation and angle of attack ofthe adjustable nose assembly when the sensors detect that the sensordevice is held up as it moves down the wellbore. A similar design isdescribed in US patent U.S. Pat. No. 7,757,782. This device is also anactive system which requires manipulation from an operator at thesurface to change the nose angle and azimuth in order in order tonavigate past obstacles after the logging tool is obstructed.

It would be an advantage to have an improved logging tool assemblycomprising sensor transportation apparatuses to carry the assembly downa wellbore which addressed any or all of the above issues or at leastprovided an alternative choice. An improved logging tool assembly withsensor transportation apparatuses and orientation structure which couldalso be used to orient the logging tool assembly would also be ofadvantage.

The reference to any prior art in the specification is not, and shouldnot be taken as, an acknowledgement or any form of suggestion that theprior art forms part of the common general knowledge in any country.

DISCLOSURE OF INVENTION

According to one aspect of the present invention there is provided alogging tool assembly comprising:

-   -   an elongate sensor assembly,    -   a plurality of sensor transportation apparatuses for        transporting the elongate sensor assembly through a wellbore,        the sensor transportation apparatuses spaced apart along the        elongate sensor assembly, wherein each sensor transportation        apparatus comprises:        -   an engagement structure to connect the sensor transportation            apparatus to the elongate sensor assembly and prevent            relative rotation between the sensor transportation            apparatus and the elongate sensor assembly, and        -   one or more pairs of wheels arranged to rotate on an axis of            rotation substantially perpendicular to a longitudinal axis            of the elongate sensor assembly,    -   wherein the axes of rotation of the pairs of wheels of said        transportation apparatuses are parallel, and    -   an orientation structure connected to the elongate sensor        assembly to prevent relative rotation between the orientation        structure and the elongate sensor assembly, the orientation        structure comprising at least one radially extending orientation        projection, in a transverse outline of the logging tool assembly        a said orientation projection extending between the pair of        wheels so that the shortest distance between a centre of gravity        of the elongate sensor assembly and the wellbore wall is when        the logging tool assembly is on the wheels of the transportation        apparatuses.

In some embodiments, there is a single most stable orientation withinthe wellbore with the logging tool assembly on the wheels of thetransportation apparatuses and with the elongate sensor assembly closestto the low side of wellbore wall.

In some embodiments, each wheel has a diameter substantially greaterthan one of the diameter, width or height of the elongate sensorassembly.

In some embodiments, in a transverse view of the logging tool assemblythe elongate sensor assembly is carried between the pair of wheels.

In some embodiments, the elongate sensor assembly comprises a samplingtool oriented to take a sample from a desired side of the wellbore withthe logging tool assembly in the stable position

In some embodiments, the elongate sensor assembly comprises a samplingtool oriented to take a sample from a horizontal side of the wellborewith the logging tool assembly in the stable position.

In some embodiments, the elongate sensor assembly comprises a samplingtool oriented to take a sample from a high-side of the wellbore with thelogging tool assembly in the stable position.

In some embodiments, the elongate sensor assembly comprises a samplingtool oriented to take a sample from a low-side of the wellbore with thelogging tool assembly in the stable position.

In some embodiments, in the stable position, the axes of rotation of theplurality of sensor transportation devices are above the centre of massof the elongate sensor assembly with the logging tool assembly in thestable position.

In some embodiments, the axes of rotation of the plurality of sensortransportation devices are on or below the centre of mass of theelongate sensor assembly with the logging tool assembly in the stableposition.

In some embodiments, the orientation projection is a bow-springeccentering device.

In some embodiments, the orientation structure comprises a poweredorientation projection moveable between an extended or raised positionand a retracted or lowered position.

In some embodiments, lateral extremities of the at least one orientationprojection and the bottom of the wheels present lateral extremities ofthe transverse outline of the logging tool assembly.

In some embodiments, lateral extremities of the at least one orientationprojection and the top and bottom of the wheels present lateralextremities of the transverse outline of the logging tool assembly.

In some embodiments, the lateral extremities of the transverse outlineof the logging tool assembly have a rotational centre that is offsetfrom the centre of mass of the elongate sensor assembly so that thesensor transportation apparatus is oriented in the most stable positionwith the centre of mass of the elongate sensor assembly below therotational centre.

In some embodiments, the pair of wheels are integrally formed as asingle wheel providing two spaced apart edges to contact the well borewall.

According to another aspect of the present invention, there is provideda logging tool assembly comprising:

-   -   an elongate sensor assembly,    -   a plurality of sensor transportation apparatuses for        transporting the elongate sensor assembly through a wellbore,        the sensor transportation apparatuses spaced apart along the        elongate sensor assembly, wherein each sensor transportation        apparatus comprises:        -   an engagement structure to connect the sensor transportation            apparatus to the elongate sensor assembly and prevent            relative rotation between the sensor transportation            apparatus and the elongate sensor assembly, and        -   one or more pairs of skids arranged parallel to a            longitudinal axis of the elongate sensor assembly, and            an orientation structure connected to the elongate sensor            assembly to prevent relative rotation between the            orientation structure and the elongate sensor assembly, the            orientation structure comprising at least one radially            extending orientation projection, in a transverse outline of            the logging tool assembly a said orientation projection            extending between the pair of skids so that the shortest            distance between a centre of gravity of the elongate sensor            assembly and the wellbore wall is when the pair of skids of            the transportation apparatus is in contact with the wellbore            wall

In some embodiment, there is a single most stable orientation within thewellbore with the logging tool assembly on the skids of thetransportation apparatuses and with the elongate sensor assembly closestto the low side of wellbore wall.

In some embodiment, lateral extremities of the at least one orientationprojection and the skids present lateral extremities of the transverseoutline of the logging tool assembly.

According to another aspect of the present invention there is provided asensor transportation apparatus to convey an elongate sensor assemblythrough a wellbore, the sensor transportation apparatus comprising:

-   -   at least one engagement structure to connect the sensor        transportation apparatus to the sensor assembly, and    -   one or more wheels arranged to rotate about an axis of rotation        substantially perpendicular to a longitudinal axis of the sensor        assembly when the transportation apparatus is connected to the        sensor assembly, and    -   an orientation structure defining a form having a transverse        outline which has a rotational centre, wherein the rotational        centre is offset from a centroidal axis of the elongate sensor        assembly.

In some embodiments, the lateral extremities of the orientationstructure substantially lie on a substantially circular imaginary curvewhich is centred at the rotational centre.

In some embodiments, the sensor transportation apparatus has only onestable orientation.

In some embodiments, the wheels are shaped and dimensioned such that, inuse, contact between each wheel and the wellbore wall is at a surface ofthe wheel which is at the radial extremity of the wheel, relative to theaxis of rotation.

In some embodiments, each said wheel extends below the sensor assemblyand the engagement structure when the sensor transportation apparatus isin a substantially horizontal orientation.

In some embodiments, a rotational axis of each said wheel is above thecentroidal axis of the tool-string when the sensor transportationapparatus is in a substantially horizontal orientation.

In some embodiments, the rotational axes of the wheels are substantiallyparallel and coplanar.

In some embodiments, at least two of the wheels have a common axis ofrotation.

In some embodiments, the wheels are mounted on stub axles.

In some embodiments, the orientation structure comprises at least onelaterally extending orientation projection.

In some embodiments, the orientation structure further comprises atleast one of the wheels.

In some embodiments, the wheels run on bearings and the apparatusfurther comprises a lubrication delivery apparatus which provides alubricant to the bearings at a pressure which is greater than ambientwellbore pressure.

In some embodiments, the engagement structure engages an exteriorsurface of the sensor assembly.

In some embodiments, the engagement structure partially encloses theexterior surface of the sensor assembly without completely encirclingthe sensor assembly.

In some embodiments, a portion of the sensor assembly extends below theengagement structure when the sensor transportation apparatus is in asubstantially horizontal orientation.

In some embodiments, the engagement structure is adapted for in-lineconnection to the sensor assembly.

In some embodiments, the transportation apparatus further comprises adrive means, wherein at least one of the wheels is connectable to thedrive means.

In some embodiments, the apparatus further comprises a clutch betweenthe drive means and each driven wheel.

In some embodiments, the apparatus further comprises a jockey wheelmounted to adjustable mounting means for selectively raising or loweringthe jockey wheel.

In some embodiments, when the mounting means are raised, the jockeywheel engages an opposite side of the wellbore to the wheels.

According to another aspect of the present invention there is provided asensor transportation apparatus to convey an elongate sensor assemblythrough a wellbore, the sensor transportation apparatus comprising

-   -   at least one engagement structure to connect the sensor        transportation apparatus to the sensor assembly, and    -   one or more wheels arranged to rotate on bearings about an axis        of rotation substantially perpendicular to a longitudinal axis        of the sensor assembly when the transportation apparatus is        connected to the sensor assembly, and a lubrication delivery        apparatus which provides a lubricant to at least one of the        bearings at a pressure which is maintained at greater than        ambient wellbore pressure.

In some embodiments, the bearing comprises a ball bearing assembly or abush bearing assembly.

In some embodiments, the lubrication delivery apparatus comprises areservoir comprising an elastic diaphragm.

In some embodiments, the reservoir comprises a volume between an innersurface of the reservoir and a base structure.

In some embodiments, the base structure comprises an outer surface ofthe transportation means.

In some embodiments, an exterior side of the diaphragm is subject toambient pressure.

In some embodiments, each wheel is mounted to a stub axle.

In some embodiments, the lubrication delivery apparatus comprises alubrication channel in each said stub axle.

In some embodiments, an outer end of each said stub axle engages alongitudinally extending protection structure.

According to another aspect of the present invention there is provided asensor transportation apparatus to convey a sensor assembly through awellbore, the apparatus comprising

-   -   a body to connect to said sensor assembly,    -   one or more wheels arranged to rotate on respective stub axles        about an axis substantially perpendicular to the longitudinal        axis of said sensor assembly when the body is connected to said        sensor assembly,    -   wherein one or more stub axles are supported by an orientation        projection, or wherein one or more wheels are protected by an        orientation projection.

In some embodiments, the orientation projection extends in front of thewheel which is connected to the respective stub axle.

In some embodiments, the orientation projection extends longitudinallyto a point behind the wheel which is connected to the respective stubaxle.

In some embodiments, the wheel extends above and below the orientationprojection.

In some embodiments, the orientation projection extends around the wheeland is connected to the body.

In some embodiments, the orientation projection is removeably connectedto the body.

According to another aspect of the present invention there is provided abase for a guide device for guiding a tool-string comprising an elongatesensor assembly in a wellbore, the base comprising a first engagementportion for engaging an end of the tool-string and second engagementportion for engaging a nose assembly, wherein the base is shaped suchthat a nose assembly engaged, in use, with the second engagement portionprojects away from the base at an angle which is offset to alongitudinal axis of the tool-string engaged, in use, with the firstengagement portion.

In some embodiments, the base is formed as an integral element orcomponent of one end of an orientation structure.

In some embodiments, the base is hollow or has an aperture therethrough.

According to another aspect of the present invention there is provided aguide device for guiding a tool-string in a wellbore, the tool-stringprovided, in use, with an orientation structure for orientating thesensor assembly in the wellbore, the guide device comprising a noseassembly having a base adapted to engage an end of the tool-string and anose section arranged to project away from the base at a fixed anglewhich is offset to a longitudinal axis of the tool-string when the noseassembly is engaged with said tool-string.

In some embodiments, the fixed angle can be pre-set.

In some embodiments, the fixed angle can be pre-set to one of aplurality of predefined settings.

In some embodiments, the guide device comprises a locking pin engagablewith the base and the nose assembly to lock the nose section at aselected angular setting.

In some embodiments, the nose assembly comprises a locking memberprovided with a plurality of locking pin apertures and the basecomprises a plurality of locking pin apertures.

In some embodiments, the angle can be pre-set to between 1° to 60°.

In some embodiments, the angle can be pre-set to between 1° to 45°.

In some embodiments, the angle can be pre-set to between 1° to 20°.

In some embodiments, the angle can be pre-set to between 1° to 9°, morepreferably between 3° to 9°.

In some embodiments, the nose section is formed from a resilientflexible material

In some embodiments, the material is a resilient elastomer material.

In some embodiments, the nose section is made from a material which isreadily drillable by standard wellbore drilling equipment, for examplenylon.

According to another aspect of the invention there is provided a guidedevice for guiding a tool-string in a wellbore, the guide devicecomprising a nose assembly having a base adapted to engage an end of thetool-string and a nose section having a tip which is offset from alongitudinal axis of the tool string when the nose assembly is engagedwith said tool-string.

According to another aspect of the present invention there is provided atool-string provided with the sensor transportation apparatus of thefirst, second or third aspect and/or the guide device of the fifth orsixth aspect.

According to another aspect of the present invention there is provided atool-string provided with a sensor transport apparatus for transportingan elongate sensor assembly through a wellbore, and an orientationstructure, wherein

-   -   the sensor transportation apparatus comprises at least one        engagement structure to connect the sensor transportation        apparatus to the sensor assembly, and one or more wheels        arranged to rotate about an axis of rotation substantially        perpendicular to a longitudinal axis of the sensor assembly when        the transportation apparatus is connected to the sensor        assembly, and wherein    -   the orientation structure defines a form that has a transverse        outline which has a rotational centre which is offset from a        centroidal axis of the elongate sensor assembly.

In some embodiments, the engagement between the sensor transportationapparatus and the sensor assembly substantially prevents relativerotation between the sensor transportation apparatus and the sensorassembly about the longitudinal axis of the sensor assembly.

In some embodiments, the orientation structure comprises a plurality ofseparate components.

In some embodiments, the sensor transportation assembly comprises atleast one of the separate components of the orientation structure.

According to another aspect of the present invention there is provided asensor transportation apparatus to convey an elongate sensor assemblythrough a wellbore, the sensor transportation apparatus comprising:

-   -   at least one engagement structure to connect the sensor        transportation apparatus to the sensor assembly, and    -   at least one friction reduction element for reducing friction        between the apparatus and the wellbore wall, and    -   an orientation structure defining a form having a rotational        centre, wherein the rotational centre is substantially parallel        to and offset from a centroidal axis of the elongate sensor        assembly.

In some embodiments, the friction reduction element comprises at leastone skid.

In some embodiments, the friction reduction element comprises at leastone wheel arranged to rotate about an axis of rotation which issubstantially perpendicular to a longitudinal axis of the sensorassembly when the transportation apparatus is connected to the sensorassembly.

According to another aspect of the present invention there is provided atransportation apparatus comprising at least one engagement structure toconnect the sensor transportation apparatus to the sensor assembly, and

one or more wheels arranged to rotate about an axis of rotationsubstantially perpendicular to a longitudinal axis of the sensorassembly when the transportation apparatus is connected to the sensorassembly, andat least one protection structure which extends longitudinally aroundthe wheel, to thereby substantially prevent a side of the wheel fromcontacting the wellbore wall, wherein the wheel extends above and belowthe protection structure.

In some embodiments, each wheel is mounted on an axle, more preferably astub axle.

In some embodiments, each stub axle is engaged with a protectionstructure. Alternatively, the stub axle is integral with the protectionstructure.

In some embodiments, the wheel is mounted on an axle, and the protectionstructure has a height which is at least equal to a diameter of theaxle, but less than a radius of the wheel.

In some embodiments, there is a clearance space between a surface ofwheel which is at the radial extremity of the wheel, relative to theaxis of rotation, and a body of the transportation apparatus, of atleast 4 mm.

In some embodiments, there is a clearance space between a surface ofwheel which is at the radial extremity of the wheel, relative to theaxis of rotation, and an inner surface of the protection structure, ofat least 4 mm, or preferably at least 10 mm, more preferablysubstantially 19 mm.

In some embodiments, the protection structure is an orientationprojection.

According to another aspect of the present invention there is providedan apparatus for supporting, orienting and transporting an elongatesensor assembly in a wellbore, the apparatus comprising a body having atleast one engagement structure releasably attachable to the sensorassembly and an orientation structure having one or more radialprojections formed from the body corresponding to a substantiallyconstant radius from a rotational centre,

wherein the rotational centre is offset from a centroidal axis of theelongate sensor assembly such that the eccentric mass of the sensor bodycauses the tool assembly to orientate toward the lower aspect of thewellbore.

According to a further aspect of the present invention there is provideda method of taking a wellbore measurement from an upper surface of awellbore comprising positioning a sensor provided with an orientationstructure as herein described inside the wellbore and operating thesensor to take the measurement.

According to a further aspect of the present invention there is providedan elongate sensor transportation apparatus substantially as hereindescribed with reference to any one or more of the embodiments describedherein and illustrated in the drawings.

According to a still further aspect of the present invention there isprovided a guide device for guiding a tool-string substantially asherein described with reference to any one or more of the embodimentsdescribed herein and illustrated in the drawings.

The invention may also be said broadly to consist in the parts, elementsand features referred to or indicated in the specification of theapplication, individually or collectively, in any or all combinations oftwo or more of said parts, elements or features, and where specificintegers are mentioned herein which have known equivalents in the art towhich the invention relates, such known equivalents are deemed to beincorporated herein as if individually set forth.

Further aspects of the invention, which should be considered in all itsnovel aspects, will become apparent from the following description givenby way of example of possible embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

An example embodiment of the invention is now discussed with referenceto the drawings in which:

FIG. 1 shows a isometric view of a sensor transportation apparatus asconfigured in accordance with a preferred embodiment of the invention.

FIG. 2 shows a side view of the transportation apparatus of FIG. 1

FIG. 3 shows a top view of the transportation apparatus of FIGS. 1 and2.

FIG. 4 shows a cross-section along plane A-A of the transportationapparatus of FIGS. 1-3, and shows the integral lubrication deliveryapparatus. The wellbore wall is shown in outline.

FIG. 5 shows a cross-section of an alternative embodiment along planeA-A. The wellbore wall is shown in outline.

FIG. 6a shows a front view of a transportation apparatus provided inaccordance with an alternative embodiment to that shown in FIGS. 1-5,with the wellbore shown outline.

FIG. 6b shows a perspective view of the transportation apparatus of FIG.6 a.

FIG. 7 shows a perspective view of a wireline tool-string engaged withboth the transportation apparatus illustrated in respect to FIGS. 6a and6b in addition to the apparatus shown with respect to FIGS. 1-4.

FIG. 8 shows an isometric view of a further embodiment of thetransportation apparatus.

FIG. 9 shows a cross-section view of the embodiment shown in FIG. 8.

FIG. 10 shows a side view of a guide device provided in accordance withone embodiment of the invention.

FIG. 11 shows a front perspective view of the guide device of FIG. 10.

FIG. 12 shows a rear perspective view of the guide device of FIG. 10.

FIG. 13 shows an exploded side view of another embodiment of the guidedevice.

FIG. 14 shows an exploded perspective view of the guide device of FIG.13.

FIG. 15 shows an isometric view of a base for a guide device.

FIG. 16 shows a perspective view of an embodiment of an adjustable guidedevice set to a 3° angle.

FIG. 17 shows the adjustable guide device of FIG. 16 set to an 8° angle.

FIG. 18 shows the adjustable guide device of FIG. 16 set to a 15° angle.

FIG. 19 shows exploded perspective view of another embodiment of anadjustable guide device.

FIG. 20 shows an isometric view of an orientation structure which isprovided with low friction skids.

FIG. 21 shows an isometric view of another embodiment of an orientationstructure which is provided with low friction skids.

FIG. 22 shows an isometric view of another embodiment of an orientationstructure which is provided with low friction skids.

FIG. 23 shows an isometric view of another embodiment of an orientationstructure which is provided with low friction skids.

FIG. 24 shows a transverse cross-section of another embodiment of anorientation structure which is provided with low friction skids.

FIG. 25 shows a transverse cross-section of another embodiment of anorientation structure which is provided with low friction skids.

FIG. 26 shows a transverse cross-section of another embodiment of anorientation structure which is provided with low friction skids.

FIG. 27 shows a transverse cross-section of another embodiment of anorientation structure which is provided with low friction skids.

FIG. 28 shows a perspective view of a guide device and orientationstructure mounted to a wireline logging tool-string.

FIG. 29 shows a perspective view of the guide device of FIG. 28 incombination with an alternative orientation structure which is providedwith low friction skids, mounted to a wireline logging tool-string.

FIG. 30 a perspective view of the guide device of FIG. 28 in combinationwith two orientation structures which are provided with low frictionskids mounted to a wireline logging tool-string.

FIG. 31 a perspective view of the guide device of FIG. 28 in combinationwith transportation apparatus mounted to a wireline logging tool-string.

FIG. 32 shows a perspective view of a weight bar attached to a guidedevice according to FIG. 19 and three transport apparatus according toFIG. 41.

FIG. 33 shows a perspective view of a guide device according to FIG. 19attached to a wireline tool-string, with a bowspring orientationstructure.

FIG. 34 shows a perspective view of another embodiment of the guidedevice.

FIG. 35 shows a perspective view of a transportation apparatus with anintegral lubrication delivery apparatus with one wheel and associatedbearing shown in partially exploded form.

FIG. 36 shows a perspective view of the transportation apparatus inanother embodiment.

FIG. 37 shows an isometric view of a transport apparatus configured as atractor unit, with a jockey wheel in a raised position.

FIG. 38 shows a front view of the tractor unit of FIG. 37 in use in awellbore, with a lower portion of the jockey wheel shown in hiddendetail.

FIG. 39 shows a front view of the tractor unit of FIG. 37 in use in awellbore with the jockey wheel in a lowered position, and with a lowerportion of the jockey wheel shown in hidden detail.

FIG. 40 shows a perspective view of another embodiment of an orientationstructure.

FIG. 41 shows a perspective view of a guide device and orientationstructure mounted to a wireline logging tool-string which has a samplingtool on its upper surface.

FIG. 42 shows the same wireline logging tool-string as FIG. 42, but withwheeled transportation providing the orientation.

FIGS. 43A and 43B show a logging tool assembly 100 comprising aplurality of transportation apparatuses 1 and an orientation structure24 mounted to an elongate sensor assembly 2. FIG. 43A is a perspectiveview from above and FIG. 43B is a transverse end view with the loggingtool assembly 100 in a most stable position.

FIGS. 44A and 44B show another logging tool assembly 100 comprising aplurality of transportation apparatuses 1 and an orientation structuremounted to an elongate sensor assembly 2. FIG. 44A is a perspective viewfrom above and FIG. 44B is a transverse end view with the logging toolassembly 100 in a most stable position.

FIGS. 45A and 45B show another logging tool assembly 100 comprising aplurality of transportation apparatuses 1 and an orientation structure24 mounted to an elongate sensor assembly 2. FIG. 45A is a perspectiveview from above and FIG. 45B is a transverse end view with the loggingtool assembly 100 in a most stable position.

FIGS. 46A and 46B show another logging tool assembly 100 comprising aplurality of transportation apparatuses 1 and an orientation structure24 mounted to an elongate sensor assembly 2. FIG. 48A is a perspectiveview from above and FIG. 48B is a transverse end view with the loggingtool assembly 100 in a most stable position.

FIGS. 47A to 47D show another logging tool assembly 100 comprising aplurality of transportation apparatuses 1 and an orientation structure124 mounted to an elongate sensor assembly 2. FIG. 47A is a perspectiveview from above, FIG. 47B is a transverse end view with the logging toolassembly 100 in a most stable position, FIG. 47C is a bottom view, andFIG. 47D is a side view.

BEST MODES FOR CARRYING OUT THE INVENTION

FIGS. 1-4 show a number of views of the transportation apparatus 1 asprovided. In this embodiment the transportation apparatus is arranged toconnect over or on to the exterior surface of an elongate sensorassembly—shown in cross-section in FIG. 4 as a tool-string 2 used in awireline logging applications. FIG. 4 also illustrates the position ofthe longitudinal axis 2 a of the tool-string 2. As used herein thephrase “elongate sensor assembly” includes both the sensors themselves,and any equipment attached to the sensors such as weights, spacers andflexible couplings.

FIG. 4 illustrates the perimeter walls of a wellbore 3 which thetool-string 2 is to be conveyed down by the transportation apparatus 1.For the sake of convenience the wellbore 3 is shown with a substantiallyhorizontal orientation, with its low side 3 a shown at the bottom of thepage.

The transportation apparatus 1 includes the main body 4, used to mountand locate the remaining elements or components of the apparatus.

FIGS. 1 through 3 show details of a pair of engagement structures formedin this embodiment by integral locking collars 5. These locking collars5 are located at either end of the apparatus 1. Each collar 5 isarranged to partially enclose the exterior side wall surface of thetool-string 2, allowing the transportation apparatus to be slid on andover the tool-string at any desired position along the length of thetool-string. Each collar includes a series of threaded holes 5 aarranged to receive a screw which engages with a recess or blind hole inthe exterior surface of the tool-string. These threaded holes 5 a and anassociated set of screws are used to lock the apparatus 1 to thetool-string 2 with a specific orientation. By arranging the collars 5 toonly partially enclose the tool-string 2, the tool-string can be carriedin a lower position than would be possible if the collars 5 were tocompletely encircle the circumference of the tool-string 2. The bodywith threaded holes 5 a and screws provide an engagement structure toconnect the transportation apparatus to the sensor assembly and preventrelative rotation between the sensor transportation apparatus as theelongate sensor assembly.

The main body of each of these collars also defines or forms aprotection structure 14 which protects wheels deployed on either side ofthe body from impact and abrasion. These protection structures alsoserve to orientate the carriage and tool-string assembly in thewellbore. These protection structures can also prevent the space betweenthe wheel and tool-string 2 catching on wellbore projections, such asthe casing shoe, as the tool-string 2 is pulled up and out of thewellbore. As can be seen from at least FIG. 1 these protectionstructures may incorporate an angled surface projection 13 which can actto position the sensor assembly and transportation apparatus in thewellbore and guide the tool down the wellbore.

FIGS. 1 through 4 also show the provision of a pair of wheels 6 whichform part of the transportation apparatus 1. These wheels 6 are deployedlaterally adjacent to one another on opposite sides of a tool-string. Inthe embodiment shown each wheel rotates on a stub axle 7. The wheels 6have an axis of rotation which is perpendicular to a longitudinal axisof the elongate sensor assembly. In the embodiment shown, the wheelshave a common axis of rotation.

As can be seen from these figures each wheel 6 has a diametersubstantially greater than one of the diameter, width or height of thetool-string 2. This allows each of the wheels 6 to make radial contactwith the wall of the wellbore 3 (that is, the radial edge of the wheelsmakes contact with the wellbore wall). The large relative size of eachwheel 6 lifts the tool-string 2 from the low side surface of thewellbore 3, allowing the transportation apparatus 1 to convey thetool-string 2 down the wellbore 3. These large wheels allow thetransportation apparatus 1 to roll along rugose borehole walls, up andover obstructing ledges which would normally impede the progress of thewireline logging tool-string 2. The wheels are widely spaced in thewellbore with a broad wheel track which allows the wheels to bridge overobstructing wellbore cuttings which tend to sit on the low side of thehole 3 a. In preferred embodiments the wheels 6 extend below the mainbody 4 and below the sensor engaged with the apparatus, and therebycreate a minimum clear space of at least 10 mm, more preferably at least½ inch, between the tool string 2 (and the body) and the bottom of thewellbore.

FIG. 4 shows a cross-section view of the transportation apparatus ofFIGS. 1-3 along the plane A-A shown in FIGS. 2 and 3. FIG. 5 showssimilar view to FIG. 4 of a cross-section view of the transportationapparatus provided in a further embodiment. In the embodiment shown withrespect to FIG. 4 a double set of ball bearing assemblies 10 are used,whereas in FIG. 5 the wheels rotate over a set of bushes 110.

FIGS. 4 and 5 show the positioning and arrangements of the axis ofrotation of each wheel 6 as provided by stub axles 7. As can also beseen from these figures each of these stub axles 7 is located above thelongitudinal axis 2 a of the tool-string 2. The longitudinal axis isessentially the axial or longitudinal centre of mass of the tool-string.As the tool-string 2 is much heavier than the transportation apparatus 1the tool-string 2 will tend to rotate into the orientation shown in FIG.4 where the transportation apparatus sits squarely on both wheels.

Identified on these figures is the rotational centre 15 of thetransportation apparatus and the centroid 2 a or centre of mass of thetool-string. In the embodiment shown each section of the tool-string hasa centre of mass 2 a approximately in the middle of the circular sectionof the tool-string. The rotational centre 15 of the transportationapparatus is located above the centroidal axis 2 a of the tool-string.The centroidal axis of the tool-string, as that phrase is used herein,is formed by the line joining the centre of mass of each cross-sectionalong the length of the tool-string. The axis of rotation of the wheels6 preferably passes through the rotational centre 15.

The body 4 also mounts an orientation structure comprising at least oneorientation projection 8. As can be seen from FIG. 4 the orientationprojection 8 assists in providing the tool-string 2 with a predictableorientation within the wellbore 3. If the tool-string 2 were to rotateto place the orientation projection 8 in contact with the low side ofthe wellbore 3 this would make the position of the combinedtransportation apparatus and connected tool-string 2 unstable. Theorientation projection 8 therefore assists in positioning andorientating the tool-string in the arrangement shown in respect of FIG.4. The radially extreme edges of the wheels 6 and the protectionstructure 14 also form part of the orientation structure and assist inorientating the tool-string in the orientation shown in respect to FIG.4.

FIGS. 4 and 5 also show the form provided through a cross-section of thetransportation apparatus made through all of its orientation projections8, protection structures 14 and wheels 6. This form has a transverseoutline (that is an outline or silhouette when viewed along thelongitudinal axis of the sensor assembly) which has a rotational centre15. The position of this rotational centre is the point whichexperiences the minimum vertical displacement when the form is rolledover a flat horizontal surface. In preferred embodiments the extremitiesof the orientation structure lie on a substantially circular imaginarycurve centred on the rotational centre 15. The rotational centre of thetransportation apparatus is offset from the centroid or centre of massof the tool-string 2 a.

The offset between the rotational centre of the transportation deviceand centre of mass of the tool-string ensures the assembly is orientatedin the most stable position with the tool-string centre of mass belowthe rotational centre of the transportation apparatus. In this stableposition the tool-string descends down the wellbore carried on thewheels of the transportation apparatus. As shown in FIGS. 4 and 5, inthe most stable position the tool-string 2 is closest to the low side ofwellbore wall.

Referring in particular to FIG. 4, in this embodiment the rotation ofeach wheel 6 is lubricated by a pressurised lubrication system 9 as itrotates about a double set of ball bearing assemblies 10. FIG. 5 showsan alternative arrangement of the transportation apparatus where thelubrication system 9 acts on a set of bushes 110. This lubricationsystem 9 includes a lubricant reservoir 11 and pressurising plungerlinked to the bearings 10 or bushes 110 by a pair of channels 12. Inother embodiments the plunger may be replaced by a set of elastomerbellows, or by an elastic diaphragm, as is described further below. Theplunger is maintained at a higher pressure than the surrounding wellborefluids thereby force feeding lubricant to the wheel bearing or bushsurfaces via the channels 12. Pressurisation of lubricant at this pointin the apparatus prevents the entry of exterior contaminants from thewellbore 3.

FIGS. 6a and 6b show cross-section and isometric views of atransportation apparatus 201 provided in accordance with alternativeembodiment to that shown in FIGS. 1-5. FIG. 7 shows an isometric view ofa wireline tool-string 2 engaged with both the transportation apparatusillustrated in respect to FIGS. 6a and 6b in addition to the apparatusshown with respect to FIGS. 1-4.

In the embodiment of the apparatus shown in FIG. 6b the transportationapparatus 201 is arranged to engage with the bottom end or nose of atool-string, thereby forming the leading component deployed down awellbore. In this embodiment of the transportation apparatus 201includes a single wheel 206 deployed as the leading component of theapparatus. This single wheel can act as a hole finding assembly whichcan encounter and then roll over the top of obstacles immediately in thepath of the tool-string. As can also be seen from FIGS. 6a and 6b thewheel 206 has a scalloped or concave profile, allowing it to bridgecuttings and obstacles encountered in the middle of the low side of thewellbore. The wheel is scalloped to ensure that only the edges of thewheel contact the wellbore wall resulting in a wide wheel track width,lower rolling friction and greater stability in the operating position.The single wheel providing two spaced apart edges in contact with thewellbore wall may be considered as a pair of integrally formed wheels.

The axis of rotation of the wheel 206 is above the centreline orlongitudinal mid-line axis 202 a of the tool-string which defines thelongitudinal or axial centre of mass of the tool-string.

Furthermore, the apparatus 201 has an orientation structure which inthis embodiment comprises multiple orientation projections 208 arrangedto assist in maintaining this desired orientation of the tool-string.The orientation projections 208 a also function as protection structuresand protect the wheels. As can be seen in FIGS. 6a and 6b , one or moreof the orientation projections 208 a may also provide a mounting pointfor mounting the wheel 206 or wheel axle.

FIG. 6a also shows the form provided through a cross-section view of thetransportation apparatus 201 made through all of its orientationprojections 208 and the end view of wheel 206. This form has atransverse outline with a rotational centre 207. The rotational centreis substantially parallel to and offset from a central axis of theelongate sensor assembly. The rotational centre of the transportationapparatus is offset from the centroid or centre of mass of the sensorassembly/tool-string 202 a.

As with the embodiments described above, the offset between therotational centre of the transportation device and centre of mass of thetool-string ensures the assembly is orientated in the most stableposition with the tool-string centre of mass below the rotational centreof the transportation device. In this stable position the tool-stringdescends down the wellbore carried on the wheels of the transportationdevice.

FIG. 7 shows how these two different implementations of thetransportation apparatus can be deployed in conjunction with a singletool-string 2 to form a system for transporting the tool-string. Thesingle wheeled apparatus 201 is used to lift the bottom end or nose ofthe tool-string while the paired wheels of the transportation apparatus1 is used to carry the upper section of the tool-string 2. In anotherembodiment the transportation apparatus may be provided with a partialorientation structure, or no orientation structure at all. In theseembodiments a separate component may carry some or all of theorientation structure. For example, a tool-string may be provided with atransportation apparatus and one or more of the orientation structuresshown in

FIG. 20, 21 or 33. The relative positioning of the separate componentsof the orientation structure along the sensor assembly is not critical,provided the overall form has a transverse outline with a rotationalcentre.

FIGS. 8 and 9 show an alternative embodiment of the transportationapparatus 1 a. This embodiment is configured for in-line connection to asensor assembly, rather than mounting over the sensor or other sensorassembly component. As can be seen, the transportation apparatus 1 a isprovided with an orientation structure which includes a protectionstructure which includes removable orientation projections 8 a whichextend from in front of the wheels, around an exterior surface 6 a ofthe wheels 6. These orientation projections 8 a are shaped to assist inpreventing material from clogging the space between the inside surfaceof the wheel 6 b and the corresponding exterior surface of the main body4 a.

The width of the wheels 6 is preferably allows a clearance space betweenthe inner surface of the wheel and the body, and between the outersurface of the wheel and the protection structure. In a preferredembodiment there is at least 4 mm clearance between the operatingsurface of the wheels and the surrounding body and structure, as isdescribed further below.

As is best seen in FIG. 9, in this embodiment the orientationprojections 8 a also operate to support the outer ends of the stub axles7 on which the wheels 6 are mounted. Those skilled in the art willappreciate that in an alternative embodiment (not shown) the stub axles7 may be permanently connected to or integral with the removableorientation projections 8 a, and may be engaged with and supported bythe body 4 a at their inner ends.

As shown in the cross-section view of FIG. 9, the wheel 6 diameter isgreater on the inner face 6 b than the outer face 6 a to fit to thecircular wellbore profile. This variation in wheel diameter causes someskidding at the contact surface between the wheel and the wellbore wallas the wheel rotates. Preferably the wheel should be narrow in order tominimise skidding contact and provide the least friction between thewheel and the wellbore wall as the wheel rotates down the wellbore. Ascan be seen from these figures, the width of the wheels 6 is less thanabout 20 mm, preferably less than 18 mm. In one embodiment shown in FIG.9 the wheel width is 10 mm. In another preferred embodiment shown inFIG. 42 the wheel width is 15 mm.

FIGS. 10 to 12 show a number of views of a guide device 21. The guidedevice 21 includes a nose assembly 22 formed from a nose section 23 anda base 27, as shown in FIGS. 10 and 11. Directly attached to the noseassembly 22 is an orientation structure 13, provided in the embodimentshown by an orientated stand-off 24.

The orientated stand-off 24 provides a sleeve like structure with ahollow interior cavity 29 arranged to receive the leading end of thewireline logging tool-string. The orientated stand-off 24 includes apair of friction reducing elements, in this case travel skids 26, whichare oriented to slide along the downside wall of the wellbore throughthe action of a set of three orientation projections 8 provided by theorientated stand-off 24. In the embodiment shown the travel skids 26 areformed from a durable ceramic material which has low frictioncharacteristics and resists abrasion, and the effects of hightemperatures and high alkaline conditions found in a wellbore, forexample alumina ceramic or polymetallic oxide thermosetting ceramic. Inother embodiments suitable plastic or elastomer materials can also beused for this component. When provided with such friction reducingelements the orientated standoff 24 can function as a transportationapparatus, although wheels may be necessary for high deviation angles.

The travel skids, when provided, may be designed for use in a specificwellbore diameter, and may be shaped to conform to the curvature of thewellbore wall. The leading and trailing edges of the travel skids arecontoured to form a gentle entry to allow the skids to “ski” overmudcake and cuttings debris.

The travel skids are positioned on the orientated standoff so that theydo not travel over the lowermost section of the wellbore where cuttingsare likely to accumulate. Rather, the skids straddle the cuttings andare positioned laterally in on the borehole wall, preferably between 30°and 45° from a vertical plane through the longitudinal axis of thesensor assembly.

The orientation structure 24 comprising the projections 8 has anengagement structure to connect the orientation structure to thetool-string to prevent relative rotation between the structure 24 andthe tool-string. As described above, the engagement structure maycomprise threaded holes and associated screws to engage the tool-stringto lock the structure 24 to the tool string, as described with referenceto FIG. 40. As is described above with reference to FIGS. 1 to 4, theorientation projections 8 act to destabilise the position of thetool-string if placed in contact with the low side wall of a deviatedwellbore. The substantial weight of the tool-string will ensure that ifone of these projections is in contact with the down side wall, thetool-string will rotate back about it's longitudinal axis to anorientation placing the travel skids in contact with the downside wall.

As can be seen from FIGS. 10 to 12, the nose section 23 has a fixedoffset angle relative to the longitudinal axis of any tool-stringengaged with the interior cavity 29 of the orientated stand-off 24. Thisarrangement provides the nose section 23 with a permanent upwardinclination as the combined guide device and tool-string is deployeddown a deviated wellbore. The upward inclination of the nose sectionensures that the nose section tip 36 is elevated above the low side ofthe wellbore by a height 37, and is offset from and above thelongitudinal axis of the tool-string. Hence obstacles on the low sidewall of the wellbore are avoided by the guide device with thetool-string following immediately after the nose assembly.

FIGS. 13 and 14 show an exploded view of a further preferred embodimentof the guide device. The guide device includes a nose section 23, a base27 and an orientation structure 24. All three components may bepartially or fully integrated (not shown) or provided as discretecomponents as in the embodiment shown. In the embodiment shown the base27 has a fixed angle relative to the tool-string longitudinal axis andis attached directly to the leading end of the wireline loggingtool-string. The nose section 23 is attached to the terminal end of thebase 27. The orientation structure slides over and is attached to thelogging tool-string such that the orientation projections are aligned toorient the nose section 23 upwards as the tool-string descends down thewellbore.

The nose section 23 can be implemented in different lengths, therebyaltering the height 37 from the bottom of the wellbore to the nosesection tip 36. The offset of the nose section tip 36 is pre-setdepending on the wellbore size and conditions.

An enlarged view of one embodiment of the base 27 is shown in FIG. 15.The base 27 may be used with some nose sections of the prior art inorder to provide improved performance, although those skilled in the artwill appreciate that the tool-string will require some type oforientation structure, for example an orientated stand-off, bow springeccentraliser and/or transportation apparatus as described herein, inorder to orientate the nose away from the base of the wellbore.

The base 27 has a first engagement portion 25 a for engaging an end of atool-string, and a second engagement portion 25 b for engaging a noseassembly. The engagement portions have centrelines which are angularlyoffset, such that a nose assembly engaged, in use, with the secondengagement portion 25 b has a centreline which extends at an angle tothe centreline of a tool-string engaged with the first engagementportion 25 a, as can be seen in FIG. 13. The offset angle maybe anysuitable angle, depending on the length of the nose assembly and thediameter of the wellbore, as is described further below.

In this embodiment the first engagement portion 25 a is provided as acollar which fits over a standard boss provided at the end of atool-string, and the second engagement portion 26 b is provided as ahollow boss having standard outer dimensions for engaging a collarprovided at the end of a prior art nose assembly. The base 27 is itselfhollow, or at least has an aperture therethrough, to allow wiring to bepassed through the base 27 if necessary.

FIGS. 16 to 18 show different configurations of angle nose assemblycapable of being used in the embodiments shown in FIGS. 28-33. The noseassembly can rotate or pivot about an axle 38 which is engaged to thebase 27, so that the angle of the nose assembly can be pre-set to aselected angle before the tool-string is lowered into the wellbore. Thebase 27 has a locking arm (not shown) extending inside the nose section23. The nose section is set at a fixed pre-set angle from thelongitudinal tool axis by a locking pin extending through one of threelocking points 30 to connect with the locking arm. The nose sectionpivoting connection 38, combined with the locking point 30, secures thenose section to the base 27 at a fixed angle from the tool-stringlongitudinal axis. The selection of locking point 30 will determine theoffset angle and hence the heights 37 of the nose section tip 36 abovethe low side of the wellbore.

As can be seen from FIGS. 16-18, each fixed angle setting of the noseassembly 22 provides the nose section 23 with a different offset angle.The offset angle implemented by each nose section 23 increases from 3°in FIG. 16, 8° in FIG. 17 and 15° and FIG. 18. Those skilled in the artwill appreciate that the pre-set angle may be adjusted depending on thediameter of the wellbore, the required standoff of the tool-string inthe wellbore, and the length of the nose assembly, to locate the end ofthe nose assembly in a suitable position in the wellbore. Longer noseassemblies will require shallower angles, and shorter nose assemblieswill require larger angles, for a given wellbore diameter and standoffdistance. The angle is selected such that the tip of the nose section isabove the longitudinal axis of the tool-string.

FIG. 19 shows an alternative embodiment of an adjustable nose assembly.In this embodiment the nose section 23 is provided with a locking member31. A pin or axle 38 extends through apertures in the base 27 and thelocking member 31. The base 27 has a vertically orientated longitudinalslot 33 to accommodate the locking member 31.

The end of the locking member 31 is provided with a plurality of lockingpin apertures 34 a which are parallel to the aperture for the axle 38.Locking pin apertures 34 b are also provided in the base 27. The lockingpin apertures 34 a, 34 b are arranged such that one of the apertures 34a in the locking member 31 is aligned with one of the apertures 34 b inthe base 27 when the nose section 23 is set to one of a predeterminednumber of angles. The nose section 23 is held at the required angle byinserting a locking pin 34 through apertures 34 a, 34 b. In a preferredembodiment the apertures 34 a, 34 b are arranged to allow the nosesection to be set to angles of 3 degrees, 6 degrees or 9 degrees to thecentreline of the tool-string, although other embodiments may provideangles up to 60°, 45° or 20°. Angles as low as 1° may be used in someembodiments, although often this will require the use of aninconveniently long nose assembly.

FIGS. 20-23 show perspective views of two different types of orientationstructure provided in accordance with a yet further embodiment. Thesefigures again illustrate the different forms of orientated stand-off 24which are to be provided as orientation structures for orienting a toolstring or guide device.

These different orientated stand-offs cater for different sizes ordiameters of wellbore size. These figures also illustrate differentarrangements of orientation projections 8.

The stand-offs shown in FIG. 20 and FIG. 22 employ a set of fourorientation projections 8, while the stand-offs 24 shown in FIGS. 21 and23 employ three orientation projections only. The orientationprojections 8 have tapered extremities 35 (at upper and lower ends withthe tool string vertically run down a well bore) to assist in guidingthe tool-string around or past obstacles encountered in a wellbore.

The oriented standoffs have a hole 29 passing through the body of thedevice. This hole is offset from the nominal centre of the standoff. Theoriented standoff is designed to slip over a cylindrical wirelinelogging tool which is then fixed within the hole 29, and below therotational centre of the stand-offs. The tool-string will therefore beconveyed with a predictable orientation, which in turn will impart anupward orientation or angle to the nose section of the nose assembly.

FIGS. 24-27 show a series of transverse or cross-section views of anumber of different implementations of orientation structures. Theseorientation structures are capable of being used in the embodimentsshown with respect to FIGS. 10-19 and 28-30. Identified on these figuresis the rotational centre 15 of the orientation structure and thecentroid 2 a or centre of mass of the tool-string. In the embodimentshown each section of the tool-string has a centre of mass 2 aapproximately in the middle of the circular section of the tool-string.

These figures also show the form provided through a transversecross-section of each orientated stand-off made through all of itsorientation projections 8 (which in these embodiments also correspondsto the transverse outline). The form provided by this cross sectiontherefore has rotational centre 15. The rotational centre of theoriented standoff is offset from the centroid or centre of mass of thetool-string 2 a.

In a deviated wellbore the tool-string will naturally rotate about itslongitudinal axis to seek the most stable position. The most stableposition is where the tool-string and oriented standoff assembly has thelowest centre of gravity. The lowest centre of gravity is where the toolcentroid is below the centre of rotation. In this stable position, theguide device nose section is orientated upwards, the low-friction travelskids of the orientated standoff are in contact with the low side of thewellbore and the logging tool sensors can be optimally orientated tomeasure the preferred side of the wellbore.

These views show various arrangements of orientated stand-offs withdifferent numbers of orientation projections 8. As can be seen fromthese figures an orientated stand-off may be implemented with a numberof different arrangements of orientation projection. These projectionscan also be formed with a variety of lengths to accommodate a range ofdifferent wellbore diameters.

As can also be seen from the embodiment displayed in these figures, inthese embodiments the extremities of each of the orientation projections8 define sections of the perimeter of a substantially circular curvecentred on a point above the centre of gravity of any tool-stringengaged with the orientation structure. In the embodiments shown, eachof the projections 8 is arrayed at an equal angle to that of itsneighbouring projections. However, the travel skids 26 are preferablyarranged to have a greater spacing between them than the spacing betweenthe other orientation projections, in order to maximise the stability ofthe apparatus when it is in its preferred orientation.

FIGS. 28-31 demonstrate the use of the guide device. The figures showthe guide device displayed in FIGS. 16-18 and an associated wirelinelogging tool-string. These figures show a variety of embodiments wherean orientation structure 24 or structures are connected to a tool-string2 at positions remote from a nose assembly 22.

FIG. 28 illustrates the use of a single orientation structure, shown inthis embodiment by an orientated stand-off 24 which is connected somedistance away from a nose assembly 22. FIG. 29 illustrates a similaralternative arrangement of orientated stand-off 24 which is arranged tobe deployed in a larger diameter wellbore than the stand-off shown withrespect to FIG. 28, and hence has the nose 23 set at a larger angle anduses a larger diameter orientation structure.

FIG. 30 shows in a further embodiment which employs a pair of orientatedstand-offs 24 located at two different positions along the length of atool-string 2.

In the embodiment shown in FIG. 31 a pair of transportation apparatus 1are used to orientate the guide device 21. The transportation apparatus1 again act to provide the tool-string 2 with a predictable orientationand to impart an upward inclination to the nose section 23 of the noseassembly 22, as is described above with reference to FIGS. 1-9. Two ormore transportation apparatuses may be provided to the tool-stringdepending on its length, to support the tool string along its length tobe held above the low-side of the wellbore. As described earlier, eachtransportation apparatus is connected to the tool string via anengagement structure to prevent rotation between the transportationapparatus and the elongate sensor assembly. As shown in

FIG. 31, the transportation apparatuses 1 are fixed to the tool-stringin the same orientation. Thus, the axles and axes of rotation of thewheels of the transportation apparatuses spaced apart along the elongatesensor are parallel in a transverse view of the tool-string assembly.One skilled in the art will understand that FIG. 4 provides a transversecross sectional view through the axis of rotation of the wheels of thetransportation apparatus nearest the guide 22 back towards the apparatusfurthest from the guide. In FIG. 31 the axles are parallel and alignedto be colinear, i.e. the rotational axes are in plane.

FIG. 32 shows a variation of the system shown in FIG. 31. In thisembodiment the transport apparatus 1 are attached to a weight bar 39.The weight bar 39 is attached to a tool-string 2, preferably by aflexible coupling. This allows the transport apparatus 1 and guidedevice 21 to be used with any type of tool-string, including those withsensors that must be touching the borehole wall, those with irregularprofiles, and exceptionally large diameter tools relative to thewellbore diameter. Tools that require lateral movement in the wellboreduring operation may also be used, for example sampling tools which moveacross wellbore when set, and imager tools that are run in holecollapsed and open out to be centralised when deployed.

FIG. 33 shows another embodiment in which the orientation structureincludes the use of a bowspring eccentraliser as an orientationprojection 8. Bowspring eccentralisers are well known to those skilledin the art.

Referring next to FIG. 34, an embodiment of the guide device 21 is shownwhich has a base 27 b which has provision for mounting a temperaturesensor 40 and/or other sensor means which require direct contact withthe fluid in the wellbore. The base 27 b has a guard structure 41comprising two parallel ribs 42 arranged on either side of the sensor40, the ribs 42 extending at least as far from the body of the base 27 bas the sensor 40. This allows the temperature sensor probe to extendinto the central area of the wellbore without risk of damage resultingfrom contact with the wellbore wall. In this position the temperaturesensor assembly is well flushed by the movement of the tool through thewellbore fluids, and is not liable to be so covered with mudcake as tounduly affect response times. To ensure a fast response to temperaturechanges, preferentially the temperature sensor probe housing is madefrom a high thermal conductivity, low corrosion material such as lowBeryllium Copper alloy, silver or gold.

The temperature sensor probe is preferably thermally insulated from thebase and body of the guide device 21.

By positioning the probe at the end of the nose of the tool-string theprobe measures wellbore temperature before that temperature isinfluenced by the temperate of the tool-string itself, and mixing ofwell fluids caused by the tool-string movement.

A pressure sensor may also be provided (additionally or alternatively tothe temperature sensor). The provision of a pressure sensor which doesnot become clogged with mudcake or other debris allows the change ofdepth of the tool to be monitored. In this way the operator can ensurethat the tool-string is proceeding into the wellbore at a rate which isconsistent with the rate at which the cable feed is operating. Feedingcable at too high a rate can result in the cable becoming tangled andthe tool-string becoming difficult to remove from the wellbore.

The sensor 40 is positioned so as to be behind the upwardly angled nosesection 23. Because the orientation structures keep the nose section 23angled upward, and the nose section 23 is held at a fixed angle when inuse, the sensor 40 does not come into contact with the sides of thewellbore, and is shielded by the nose section 23 from any steps orshelves in the wellbore walls. In the embodiment shown the guide device21 is provided with the pre-set angle adjustment system described abovewith reference to FIG. 19, and shows the cover plate 43 which is used toretain the locking pin 34.

The transportation apparatus 1 may include a lubrication deliveryapparatus to provide lubrication to the wheels, as described inPCT/NZ2013/000210, which is incorporated herein by reference. Forexample, the transportation apparatus shown in FIGS. 35 and 36 isprovided with lubrication system 300. The apparatus 1 is also providedwith a protection structure in the form of removable orientationprojections 8 a which extend around an exterior surface 6 a of thewheels 6, as described above with reference to FIGS. 8 and 9. Theseorientation projections 8 a extend substantially longitudinally from infront of each wheel to behind the wheel, and are shaped to assist inpreventing material from clogging the space between the inside surfaceof the wheel 6 b and the exterior of the main body, and support theouter ends of the stub axles 7 on which the wheels 6 are mounted, as isdescribed above. As can be seen in these figures, the wheels 6 extendabove and below the longitudinally extending orientation projection 8 a.The longitudinally extending orientation projection 8 a is preferablyrelatively slender, for example having a height which is greater thanthe diameter of the axle on which the wheel is mounted, but less thanthe radius of the wheel. As is best seen in FIG. 36, a clearance spaceis provided between the radially extreme edge or surface 67 of the wheel(relative to the axis of rotation) and the longitudinal orientationprojection 8 a, although the profile of the wheel may mean that theclearance is reduced towards the centre of the wheel.

This clearance, along with the slender aspect of the protectionstructure, assists in preventing the area inside the protectionstructure from becoming clogged with debris from the wellbore surface.In a preferred embodiment there is a clearance of at least 4 mm betweenradially extreme surface 67 of the wheel (that is, the surface of thewheel which is normally in contact with the wellbore wall) and theexterior of the main body, and at least 4 mm clearance between theradially extreme edge of the wheel and the interior of the protectionstructure. In the embodiment show the interior of the protectionstructure has a clearance of at least 15 mm, more preferably at least 19mm.

The longitudinally orientated orientation projection preferably has acentral axis which is substantially coincident with the rotational axisof the wheel.

FIGS. 37 to 39 show another embodiment of the transportation apparatus,in this embodiment configured as a tractor unit.

The tractor unit 400 comprises a transportation apparatus with aplurality of main wheels 6, in this case four main wheels 6, and atleast one jockey wheel 6 c. The tractor unit preferably comprises anorientation structure having at least two orientation projections. Thoseskilled in the art will appreciate that the jockey wheel 6 c alsofunctions as an orientation projection.

The jockey wheel 6 c is preferably mounted to an adjustable mountingmeans (not shown) for raising and lowering the jockey wheel relative tothe main body 4 a. One or more of the main wheels 6, and preferably eachof the main wheels 6, are connectable to a drive means, typically one ormore electric motors. In a preferred embodiment the main wheels 6 areprovided with clutch means (not shown) which can disengage the mainwheels 6 from the drive means to allow the main wheels 6 to freewheelwhen the borehole is sufficiently steep.

In use, one or more tractor units 400 are connected in line with thetool-string. The tool-string and tractor 400 can free-wheel down thewellbore until the tool-string can no longer descend under gravityalone. At this point the jockey wheel 6 c is raised and extends upwardto make contact with the top of the wellbore wall 3 (best seen in FIG.38) thereby increasing contact pressure on the driven wheels 6. Theclutch is engaged and the main wheels 6 are driven by the drive means.In this way the tool-string can be transported along wellbores at veryhigh deviation angles, up to and including substantially horizontalwellbores. The tractor unit is preferably provided with a guide device21 as described above. One or more transportation means 1 may also beused as required to assist in transporting the tool-string.

FIG. 40 shows another embodiment of an orientation structure which isprovided as an orientated standoff 24, similar to those shown in FIGS.20 and 21. In the embodiment shown in FIG. 40, the engagement betweenthe standoff 24 and the tool-string is similar to that used with thetransportation apparatus described above with respect to FIGS. 1-3. Theengagement structure 5 is in the form of a locking collar. The collar 5is arranged to partially enclose the exterior side wall surface of thetool-string 2, allowing the standoff to be slid on and over thetool-string at any desired position along the length of the tool-string.Each collar includes a series of threaded holes 5 a arranged to receivea screw which engages with a recess or blind hole in the exteriorsurface of the tool-string. These threaded holes 5 a and an associatedset of screws are used to lock the apparatus 1 to the tool-string 2 witha specific orientation. By arranging the collars 5 to only partiallyenclose the tool-string 2, the tool-string can be carried in a lowerposition than would be possible if the collars 5 were to completelyencircle the circumference of the tool-string 2, and allows an increasedclear space 65 (preferably at least 10 mm, more preferably at least %inch) between the lower orientation projections 8, which in thisembodiment comprise low friction skids, This clear space allows thecutting debris which has collected on the bottom surface of the bore topass under the tool-string 2. As with the other orientation structuresdescribed above, the structure shown in FIG. 40 has a centre of rotationwhich is offset from the centroid of the tool-string 2.

FIGS. 42 and 43 show a variant of the system shown in FIG. 32. In thisembodiment the tool-string is provided with a prior art sampling tool 66for taking samples and pressure measurements. Because the tool-string 2is connected to at least one orientation structure, whether anorientated standoff 24 or a transportation apparatus 1, the samplingtool can be orientated to take its sample from the high side of thewellbore. This has the advantage that the high side of the wellboretends to be less damaged by the grinding action of the drillpipe as itrotates and reciprocates during the drilling operation. This damage canaffect the porosity and permeability of the wellbore wall in particular,and can lead to unrepresentative measurements, or at least delays inobtaining representative measurements. By using the apparatus shown,this sampling process is improved.

Further example embodiments are now described.

As described earlier, a logging tool-string assembly may be providedwith one or more transportation apparatuses and one or more orientationstructures. FIG. 43A illustrates an example logging tool-string assembly100 comprising an elongate sensor assembly 2 with four transportationapparatuses 1 spaced apart along its length and a single orientationstructure 24. Each transportation apparatus 1 and the orientationstructure 24 are fixed to the elongate sensor assembly 2 to preventrelative rotation, and with the axles of the transportation apparatusesparallel. Additional orientation structures could be also be fixed tothe elongate sensor assembly. FIG. 43B illustrates a transverse end viewfrom the nose end (downward end) of the logging tool assembly. With theorientation structure(s) 24 and transportation apparatus(es) 1 fixed tothe elongate sensor assembly 2, the logging tool string assembly 100presents a transverse outline with a rotational centre 15 offset fromthe centre or centre of mass 2 a of the elongate sensor assembly 2, toensure the logging tool-string assembly 100 is oriented in the moststable position with the centre of mass 2 a below the rotational centre15, as shown in FIG. 43B. In the illustrated embodiment the orientationstructure 24 has a plurality of orientation projections 8 a. The outeror lateral extremities 108 of the projections 8 lie on a substantiallycircular curve. In the transverse outline, the bottom lateralextremities 108 of the transverse outline provided by the wheels 6 alsolie on the substantially circular curve.

A curve drawn through the lateral extremities 108 of the transverseoutline has a radius of curvature substantially less than the radius ofcurvature of the wellbore wall 3. The curve has a rotational centre orcentre of curvature 15. The rotational centre is offset from the centreof mass 2 a of the elongate sensor assembly. When in the stableposition, the transverse outline of the logging tool assembly providedby the orientation structure 24 and the wheels of the transportationdevice 1 presents only two spaced apart points of contact with thewellbore wall, a contact point between the bottom of each wheel 6 andthe wellbore wall 3, as shown in FIG. 43B. There are no other points ofcontact between the transverse outline of the logging tool assembly andthe wellbore wall. With the logging tool assembly in a position otherthan the most stable position there is also one or more points ofcontact between the transverse outline of the logging tool assembly 100and the wellbore wall 3. The contact points are provided by lateralextremities of the transverse outline of the logging tool assembly 100.Here the term ‘point’ is not intended to be limited to only a precisepoint contact but to mean more generally a location or position of thewall of the wellbore.

The shortest distance between the centre of gravity 2 a of the elongatesensor assembly 2 and the wellbore wall 3 is when the pair of wheels 6of the transportation apparatus 1 is in contact with the wellbore wall3. In the most stable position with the logging tool assembly 100carried on the wheels 6, the centre of mass of the elongate sensorassembly 2 is closest to the low side of wellbore wall 3. The centre ofmass 2 a of the elongate sensor assembly 2 is further from the low sideof the wellbore wall 3 when the logging tool assembly 100 is in anyorientation within the wellbore other than the most stable position.With the logging tool oriented on its side, or up-side-down, or in anyother orientation within the wellbore other than the most stableposition, the centre of mass of the elongate sensor assembly will be agreater distance from the low side of the wellbore than when in the moststable position. This arrangement results in the mass of the elongatesensor assembly gravitating to the low side of the wellbore with thelogging tool assembly 100 on its wheels, and maintaining this moststable orientation with the elongate sensor assembly located nearest tothe low side of the wellbore, to traverse down the wellbore on itswheels.

As shown in FIG. 43B, a curve 101 having a radius of curvature equal toa radius of curvature of the wellbore wall 3 drawn between the bottom ofthe wheels 6 in the transverse outline of the logging tool assembly 100presents a first distance 102 on a radial line between the curve 101 andthe centre of mass 2 a of the elongate sensor assembly 2, and a curve101 having a radius of curvature equal to a radius of curvature of thewellbore 3 drawn between any other two adjacent lateral extremities 108of the transverse outline presents a second distance 103 between thecurve 101 and the centre of mass 2 a of the elongate sensor assembly.The first distance 102 is shorter than the second distance 103. Thisarrangement of the lateral extremities 108 of the transverse outline ofthe logging tool assembly achieves a single most stable orientation withthe assembly running on its wheels with the elongate tool string closestto the low side of the well bore.

For each orientation projection 8, a distance 105 between the lateralextremity 108 of the orientation projection 8 and the centre off mass 2a of the elongate sensor assembly 2 is greater than a distance 102 on aradial line between the centre of mass 2 a of the elongate sensorassembly 2 and a curve 101 having a radius of curvature equal to aradius of curvature of the wellbore 3 drawn between the bottom of thewheels 6 in the transverse outline of the logging tool assembly.

More or less orientation projections 8 may be provided. For example, inthe transverse view, the orientation structure 24 may present a singleorientation projection 8 that extends radially outwards between thewheels in the transverse view. In an embodiment comprising a singleorientation projection, the projection is preferably on a centreline ofthe tool-string assembly, and preferably perpendicular to the rotationalaxis of the wheels 6. The projection 8 a preferably extends radiallywith respect to the centre of rotation 15 and preferably radially withrespect to the centre 2 a of the elongate sensor assembly 2.

FIGS. 44A and 44B and FIGS. 45A and 45B present further example loggingtool-string assemblies 100 with an orientation structure 24 comprising asingle orientation projection 8 extending radially between the wheels inthe transverse view of the tool-string assembly. In the embodiment ofFIGS. 44A and 44B, the projection 8 is positioned to extend radiallybetween the wheels in a transverse outline of the logging tool assembly.In the embodiment of FIGS. 45A and 45B, the projection 8 is positionedto extend radially between the wheels and also radially outside of thelateral facing side 106 of each wheel 6 in a transverse outline of thelogging tool assembly 100. In FIGS. 45A and 45B the orientationprojection extends circumferentially around the apparatus from avertical centre of the apparatus 100 to below the axis of rotation ofthe wheels.

The orientation structure fixed to the elongate sensor assembly providesa logging tool assembly 100 with an assymetric transverse outline withrespect to the centre of mass 2 a of the elongate sensor assembly. Theassymetric transverse outline is closest to the centre of mass 2 a ofthe elongate sensor assembly 2 between the bottom of the wheels of thesensor transportation apparatus.

As shown in FIG. 44B, a distance 105 between the lateral extremity 108of the orientation projection 8 and the centre off mass 2 a of theelongate sensor assembly 2 is greater than a distance 104 between thecentre of mass of the elongate sensor assembly and an outer side 106 ofeach wheel 6 of the transportation apparatus 1.

In the embodiments of FIGS. 43A to 45B the elongate sensor assembly 2comprises a sampling tool 66 for taking samples and/or measurements fromthe wellbore and/or wellbore wall. An example of such measurements isresistivity, density or speed of sound of the rock formation penetratedby the wellbore. Samples may be the fluid contained in the pore spacesof the rock formation or cored plugs of the rock formation. In theillustrated embodiment, in the most stable position with the loggingtool-string assembly 100 positioned on the wheels 6 of thetransportation apparatuses 1, the sampling tool 66 is oriented to take asample from a high side of the wellbore.

FIGS. 47A to 47D illustrate a further embodiment of a logging toolassembly 100 comprising a plurality of transportation and an orientationstructure 124 comprising a single orientation projection 8 extendingradially between the wheels in the transverse view of the tool-stringassembly. The orientation structure 124 comprises a bow springeccentraliser, and the bow spring presents a lateral orientationprojection 8.

In the embodiment of FIGS. 47A to 47D the elongate sensor assembly 2comprises a sampling tool 66 for taking samples and/or measurements fromthe wellbore and/or wellbore wall. In the most stable position with thelogging tool-string assembly 100 positioned on the wheels 6 of thetransportation apparatuses 1, the sampling tool 66 is oriented to take asample from a low side of the wellbore. Orientation of the logging toolassembly allows for the sampling tool to be oriented to take a samplefrom any desired orientation of the wellbore, for example a horizontalside of the well bore (i.e. the high side or the low side), or any otherdesired side such as from a vertical side of the well bore 3.

In the embodiments shown in FIGS. 43A to 45B the rotational axis of thewheels extends through the centre 2 a of the elongate sensor assembly.However, the axis of the wheels may be below, on, or above the centre ofthe elongate sensor assembly. For larger wheels, the axis of rotation ispreferably above the centre of gravity 2 a of the sensor assembly. Wherethe wheels are of a size such that the top and bottom of the wheelspresent lateral extremities together with the lateral extremities of theone or more orientation projections 8 in the transverse outline of thelogging tool assembly, the rotational axis of the wheels extends throughthe rotational centre 15 of the transverse outline of the loggingtool-string assembly 100, offset from and above the centre of mass 2 aof the elongate sensor assembly 2, as shown in FIG. 43A. For smallerwheels, the top of each wheel may not present a lateral extremity of thetransverse outline of the logging tool assembly 100, in which case thelateral extremities of the transverse outline of the logging toolassembly 100 are provided by the bottom of the wheels 6 and the lateralextremities of the one or more orientation projections 8, and the axisof rotation of the wheels may be offset from the rotational centre 15 ofthe transverse outline of the logging tool assembly 100 and may be on orbelow the centre of mass 2 a of the elongate sensor assembly when thelogging tool assembly 100 is in the most stable orientation. FIGS. 47Ato 47D present an embodiment where the axis of rotation of the wheels 6is below the centre of mass 2 a of the elongate sensor assembly.

Preferably the diameter of the wheels 6 is larger than the diameter ofthe elongate sensor assembly. Preferably the diameter of the wheels isas large as possible to reduce rolling resistance over a rugose wellborewall. In alternative embodiments, one or more transportation apparatuses1 may have skids rather than wheels, on which the logging tool assembly100 is carried down the wellbore.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise”, “comprising”, and thelike, are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense, that is to say, in the sense of“including, but not limited to”.

Where in the foregoing description, reference has been made to specificcomponents or integers of the invention having known equivalents, thensuch equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and withreference to possible embodiments thereof, it is to be understood thatmodifications or improvements may be made thereto without departing fromthe spirit or scope of the appended claims.

1. A logging tool assembly comprising: an elongate sensor assembly, aplurality of sensor transportation apparatuses for transporting theelongate sensor assembly through a wellbore, the sensor transportationapparatuses spaced apart along the elongate sensor assembly, whereineach sensor transportation apparatus comprises: an engagement structureto connect the sensor transportation apparatus to the elongate sensorassembly and prevent relative rotation between the sensor transportationapparatus and the elongate sensor assembly, and one or more pairs ofwheels arranged to rotate on an axis of rotation substantiallyperpendicular to a longitudinal axis of the elongate sensor assembly,wherein the axes of rotation of the pairs of wheels of saidtransportation apparatuses are parallel, and an orientation structureconnected to the elongate sensor assembly to prevent relative rotationbetween the orientation structure and the elongate sensor assembly, theorientation structure comprising at least one radially extendingorientation projection, in a transverse outline of the logging toolassembly a said orientation projection extending between the pair ofwheels so that the shortest distance between a centre of gravity of theelongate sensor assembly and the wellbore wall is when the pair ofwheels of the transportation apparatus are in contact with the wellborewall.
 2. The assembly of claim 1, wherein there is a single most stableorientation within the wellbore with the logging tool assembly on thewheels of the transportation apparatuses and with the elongate sensorassembly closest to the low side of wellbore wall.
 3. The assembly ofclaim 1, wherein each wheel has a diameter substantially greater thanone of the diameter, width or height of the elongate sensor assembly. 4.The assembly of claim 1, wherein in a transverse view of the loggingtool assembly the elongate sensor assembly is carried between the pairof wheels.
 5. The assembly of claim 1, wherein the elongate sensorassembly comprises a sampling tool oriented to take a sample and/ormeasurement from a desired side of the wellbore with the logging toolassembly in the stable position
 6. The assembly of claim 1, wherein theelongate sensor assembly comprises a sampling tool oriented to take asample and/or measurement from a horizontal side of the wellbore withthe logging tool assembly in the stable position.
 7. The assembly ofclaim 1, wherein the elongate sensor assembly comprises a sampling tooloriented to take a sample and/or measurement from a high-side of thewellbore with the logging tool assembly in the stable position.
 8. Theassembly of claim 1, wherein the elongate sensor assembly comprises asampling tool oriented to take a sample and/or measurement from alow-side of the wellbore with the logging tool assembly in the stableposition.
 9. The assembly of claim 1, wherein, in the stable position,the axes of rotation of the wheels of the plurality of sensortransportation devices are above the centre of mass of the elongatesensor assembly with the logging tool assembly in the stable position.10. The assembly of claim 1, wherein the axes of rotation of the wheelsof the plurality of sensor transportation devices are on or below thecentre of mass of the elongate sensor assembly with the logging toolassembly in the stable position.
 11. The assembly of claim 1, whereinthe orientation projection is a bow-spring eccentering device.
 12. Theassembly of claim 1, wherein the orientation structure comprises apowered orientation projection moveable between an extended or raisedposition and a retracted or lowered position.
 13. The assembly of claim1, wherein lateral extremities of the at least one orientationprojection and the bottom of the wheels present lateral extremities ofthe transverse outline of the logging tool assembly.
 14. The assembly ofclaim 1, wherein lateral extremities of the at least one orientationprojection and the top and bottom of the wheels present lateralextremities of the transverse outline of the logging tool assembly. 15.The assembly of claim 1, wherein the lateral extremities of thetransverse outline of the logging tool assembly have a rotational centrethat is offset from the centre of mass of the elongate sensor assemblyso that the sensor transportation apparatus is oriented in the moststable position with the centre of mass of the elongate sensor assemblybelow the rotational centre.
 16. The assembly of claim 1, wherein thepair of wheels are integrally formed as a single wheel providing twospaced apart edges to contact the well bore wall.
 17. A logging toolassembly comprising: an elongate sensor assembly, a plurality of sensortransportation apparatuses for transporting the elongate sensor assemblythrough a wellbore, the sensor transportation apparatuses spaced apartalong the elongate sensor assembly, wherein each sensor transportationapparatus comprises: an engagement structure to connect the sensortransportation apparatus to the elongate sensor assembly and preventrelative rotation between the sensor transportation apparatus and theelongate sensor assembly, and one or more pairs of skids arrangedparallel to a longitudinal axis of the elongate sensor assembly, and anorientation structure connected to the elongate sensor assembly toprevent relative rotation between the orientation structure and theelongate sensor assembly, the orientation structure comprising at leastone radially extending orientation projection, in a transverse outlineof the logging tool assembly a said orientation projection extendingbetween the pair of skids so that the shortest distance between a centreof gravity of the elongate sensor assembly and the wellbore wall is whenthe pair of skids of the transportation apparatus is in contact with thewellbore wall.